Programmable circuits (e.g., field-programmable gate array (FPGA) devices) are circuits that can be configured with different designs to perform any of a variety of functions. In order to configure a programmable circuit such as an FPGA, configuration bits are generally read from an external memory module (e.g., a read-only memory (ROM)) to the configuration random access memory (CRAM) module on the programmable circuit.
However, a CRAM module is a volatile memory module that is unable to retain the information once the device or circuit is disconnected from a power source. In other words, the configuration data in the device is lost as soon as the device is powered down. A non-volatile memory is therefore generally preferable as a non-volatile memory is able to retain the configuration data, or any other information stored in the non-volatile memory, even when the device is powered down.
A one-time programmable (OTP) memory module is an example of a non-volatile memory module. Generally, external elements may cause unwanted effects in reconfigurable memory modules. For instance, ionizing radiation may cause the bits stored in the memory cells to flip undesirably. These unwanted changes are typically known as soft errors and one of the more common types of single event upsets (SEUs) that affect programmable circuits.
Compared to a reconfigurable memory module (e.g., a CRAM module), an OTP cell is typically less vulnerable to single even upsets (SEUs) as the OTP cell cannot be reprogrammed or changed in any way once it is programmed. However, a programmable device having only OTP modules, or any other read-only memory (ROM) modules for that matter, may not be desirable as the programmable device can only be configured once.
It would therefore be desirable to provide improved memory circuits for integrated circuits such as programmable devices.